Anyone got any recommendations for a car alarm setup that runs the central locking via a proximity-based key? (i.e - if the key is more than about 2m from the ignition, the car locks and the alarm engages).

I don't have a very flash car, but I like the idea of these things. Even better if it can be rigged to the ignition so that you can leave your keys in your pocket and just press the "start" button - getting a bit gimmicky at that stage though.

(Edit: Just clicked that this could probably have gone into the "gadgets" forum...)